Pump for tail production of oil

ABSTRACT

A piston pump for submerging in an oil well, consisting of four pistons that, by means of a fixed interlock ( 105 ) between two opposing pistons and a cog wheel interlock ( 104 ) between these and the two other pistons, get two oncoming piston pairs in which the mass forces are balanced. On the suction side, the pump has a valve set with a suction- and pressure valve for each of the cylinders in the bottom section; and, on the drive side, a bistable 3-5 port valve that alternately reciprocates the hydraulic oil flow from the drive unit to the one or the other cylinder pair.

The invention concerns a piston pump for oil production from oil wellshaving low pressure.

The typical oil well in the North Sea, for example, firstly has anoverpressure phase in which the oil in the structure possesses such ahigh pressure that it flows up through the production tubular by itself.This phase may last for some years, but gradually the pressure decreasessufficiently low for the well not to be self-producing any longer. Atthis stage, however, large amounts of oil remain in the structure, oftenas much as 80% of the total. There are mainly three methods ofrecovering more of the remaining amount. One method consists in gasinjection down into the annulus, causing gas and liquid to flow out in amanner similar to that of a coffee maker. Another method consists ininjecting water into the structure, thereby increasing the pressuretherein. The third method consists in introducing a pump down in thedrilling string and pumping up the oil.

Such a pump must be constructed for usage under extreme conditions.Firstly, the production tubular is of a relatively small diameter; andsecondly, it pertains to lifting heights of several thousand meters,hence very high pressures. Perhaps the biggest problem for today's pumpsis that when the pressure in the oil structure is low, the amount andvolume of gas in the oil will increase steadily, and the existing pumpsdo not function when the gas volume exceeds even a relatively smallpercentage amount.

Usually, these pumps are constructed with a large number of axial pumpson a long, joint shaft and have a motor either below or above the verypump that may be 10-20 meters long.

Onshore, for example well known from the USA, piston pumps are used inrelatively shallow wells. The piston then is generally run up and downwith a wire attached to an eccentric shaft. A pulsating oil flow, havingdelivery each time the piston moves upwards, is then achieved. This isacceptable when the oil column is this short.

Piston pumps are pressure-powerful in a single step and may, undercertain conditions, handle a relatively large amount of gas togetherwith liquid and should, based on this, be ideal for recovering a maximumamount of oil from deep wells having low pressures in the structure.Publications NO 305 667; U.S. Pat. No. 3,625,288; U.S. Pat. No.4,268,277; U.S. Pat. No. 4,536,137 and GB 2 100 362 disclose pumps basedon pistons.

In deep wells, such as those in the North Sea and other offshoreregions, oftentimes the length of the drill string is many kilometres,and commonly the geographic lifting height may be 3-5000 meters. Pumpingunder such conditions requires the oil column above the pump to flowrelatively evenly; otherwise the acceleration forces will becomeunrealistically high.

The object of invention is a piston pump for submerging in a drillingpipe, in which the pump will produce a relatively even oil flow;tolerate relatively large amounts of gas during induction; andsimultaneously having a pump with no or very small and free mass forcesthat produce vibration.

The pump according to the invention is shown in FIG. 1 and consist of,from bottom, a suction mouth piece (1), a valve housing (2), a pumpcylinder section (3), an interlock section (4), a drive cylinder section(5), a control valve housing (6) and also a hydraulic drive unit (7) ontop.

As disclosed in FIG. 2, the pump has four pistons, each respective endhaving a pump piston (101) and a drive piston (101). It is furtherdisclosed that two of the radially opposing shafts (102) of the onepiston pair is mechanically connected by means of a linkage (105), hencemove axially alike. The two other piston pairs are connected with thetwo preceding ones at cog wheel (104) and therefore will have to move inthe opposite direction of these. This provides full balancing of themass forces in the pump at the same time the volume flow becomesrelatively constant, even though a pressure surge will arise when thepistons reciprocate. On the drive side, the oil channel of the cylindersis placed below the top of the cylinder, thereby allowing the piston tostop against an oil pillow and not mechanically. In turn, the pressuresurge in this oil pillow is used to rearrange a bistable 3-5 port valvethat reciprocates the oil flow of the pistons. Thus, the drive unit hasan even oil flow through its pump.

1. A piston pump for submerging in an oil well, characterised in that ithas four pistons (101) that, by means of a fixed interlock (105) betweentwo opposing pistons and a cog wheel interlock (104) between these andthe two other pistons, get two oncoming piston pairs.